Such rotary actuators are known from the publications DE 1 200 923 B, DE 42 06 378 A1 and WO 97/28551 A1. These rotary actuators can be connected to an operating axle for the switching device and are equipped with a turning handle with a pivotable or displaceable locking member and a locking opening. The locking member interacts in the locked position with a locking member of a housing on which the turning handle is arranged. In the locked position, the locking member enables a locking means to pass through the locking opening, especially the shackle of one or several padlocks which thus lock the rotary actuator and the switching device in the switched-off position.
Thus, according to DE 42 06 378 A1, the pivotable locking member of the rotary actuator provided with the locking opening has a raised or recessed locking element which either engages the raised locking element of the housing in the locked position or locks the recessed locking element of the housing in the locked position. In the locked position, an additional lug of the locking lever engages in a hole in the operating axle and blocks movement of the turning handle.
The rotary actuator according to WO 97/28551 A1 has a locking hole passing through the turning handle housing. By moving the locking member in the form of a sliding lock in the turning handle against spring force, the locking opening is released for attaching padlocks.
A disadvantage is that this type of rotary actuator can withstand limited externally-applied forces. The locking position can be forcibly overcome and the switching device can be changed from the off position to the on position contrary to safety requirements. Thus personnel and equipment are subject to significant risks. In the case of the rotary actuator mentioned at the beginning, the use of steel parts to increase resistance, commonly used in security cylinder locks or positioning actuators in chemical plants, introduces substantial disadvantages, in particular increased production costs and expenses for the electrical grounding.